Has Anyone Ever Had Their Paid Package Returnedsender

Hey everyone!

I am a philatelist , but mainly into postal history and postcards.
I regularly buy from auction houses worldwide items of my collectors and tradesmans interest.
Middle of March, I placed several bids with one auction house in UK, but won only one lot worth 45 pounds. After few days of silence, sent a mail asking for invoice and I got it on 18th of March that stated shipment handling and insurance costs 10 pounds above my bid value, but I found it ok due to the weight. . I made the payment on 23rd of March and after some silence, I made a call on 30th of March that urged them to send my parcel on 31st of March.
Long story short, April 22. I read on tracking website parcel arrived in UK.
April 23. parcel delivered to sender UK.

Just a guess, there may be an issue with mail service to Serbia currently from the UK, due to the Pandemic. I'd contact the auction firm and see if they know what's going on. Hope you can resolve it.

Quite possibly wrongly addressed - email them to see what they put on the envelope.

I once had an item returned to me as sender. It turned out the recipient didn't know his own house number! Surprisingly the mailman in the US didn't notice the package was for someone on the same road.

Last year I purchased a stamp from some in France. The item made it to this country and then it was returned to France. The sender had placed his return address on the reverse of the envelope in a large label. Evidently, the USPS read that address as the destination and returned it to France. I have also had the address label ripped off a package to a foreign destination and returned to me two months later. Anything is possible including the discontinuance of international mail to many destinations.

A couple of years ago, I bought something from an ebay seller in Armenia, who sent the item by Registered Mail, but for some reason it got returned to him. There was no USPS tracking for it beyond New York (I live in California). When he tried again with regular airmail, it got through to me just fine.

I called the AH directly on thursday and they verified the address is correct and were stunned to have it returned to them.
Parcel tracking site showed that they sent it on 31. of march and that it sat in London until 11th of April, when it read: "arrived at destination country An Post". After that I was expecting delivery, alas...
I mean our postal service is a is excellent and efficient. Rarely do we have problems regarding international parcels/mail either incoming or outgoing.
Ironicaly, I received invoice along with fiscal slip in a regularly mailed envelope yesterday.

Since I verified with sender that the package was correctly addressed it makes me wonder who in the right mind returns a 5kg parcel sent from overseas? I mean it is not a letter. This was costly to ship.